Sliding joint for transmission lines



C. E. M CLELLAN SLIDING JOINT FOR TRANSMISSION LINES Filed July 28, 1943 May 17, 1949.

WITNESSES:

Patented May 17, 1949 Cyril -E. McClellan, Ca

tonsville, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, 'Pa., a corporation of Pennsylvania Application-July 28, 1943, Serial No. 496,520

3 Claims. 1

My invention relates to transmission lines for ultra-high frequency electric currents and, in particular, relatesto a method for providing-sliding joints by which the length of segments of such linesmay be varied.

One of the most satisfactory types of transmission lines for ultra high frequency electric currents is the so-called concentric type of line in which one line comprises the central core insulated and spaced from a surrounding sheath, both core and sheath being of conducting material. It is frequently desirable that segments of such lines shall be varied in length at will over a. substantial range, since any discontinuity in the electrical constants of the lineproduces reflected waves and resultsin resonance effects of greater or lesser degree in segments of the line intervening between such discontinuities.

By making the distance between the points of discontinuity variable, various tuning effects canv be attained as a result of such resonance, and such tuning proves to be highly desirable in certain instances.

In accordance with the prior art'the effective length of segments of concentric lines is made variable by providing sliding joints in the core and'outer sheath. In such arrangements one portion of the sheath is reduced sufiiciently in diameter to slide into and telescope in electrical contact with the other portion. The central core is similarlyiprovided with a slidingtelescopic connection by enlarging one portion and boring'it out so'that it can slide over the other portion. However, when oneportion-of the sheath or core slides telescopically within another portion the above-mentioned alteration in the outside and inside diameters of the core and sheath at the joint change the electrical constants such as self-inductanceandcapacitance per unit length of the line, and these alterations in diameter in themselves constitute a minor discontinuity in the line which would be desirable to minimize.

In accordance with my invention I avoid alteration in the exterior and-interior diameters of both the sheath and the core at a sliding joint by anovel form of conductor structure which will be described-more fully below.

One object of my invention is accordingly to provide a sliding joint for an electrical conductor which shallmaintain constancy of interior and exterior diameters of the conductor on each side of the joint.

Another object of my invention is to provide a sliding joint for transmission lines of the concentric type in which the exterior and interior diameter of the sheath and the core are maintained the same on each side of the joint.

Still another object of my invention is-to provide a form of electrical conductor for ultra-high frequency electrical transmission having asli'ding joint in which variations in the electrical conprovide a concentric transmission line for ultra high frequency current which shall have a sliding joint or joints by which itselectrical length may be varied, the joints being of such a type as to minimize the reflection of high frequency energy in crossing them.

Other objects of my invention will become apparent upon reading the following description taken in connection with the in which:

Fig. 1 illustrates the two halves of a slidable joint in a cylindrical conductor which may, for example, be the central core of a concentric transmission line.

Fig. 2 illustrates one'mem'ber of a slidable joint in a tubular type of conductor which may be the sheath of a high frequency transmission line.

Fig. 3 is a section along the line IIIIII in Fig. 2.

Fig. 4 is an elevational view of a tubular conductor adapted to cooperate with that shown in Fig. 2 to form a slidable joint and which is suitable for the sheath of a concentric transmission line; and

Fig. 5 is a section along the line VV in Fig. 4.

figures of drawings Fig. 6 is a section through a transmission line having its core portions interconnected by the joint of Fig. 1 and its sheath portions interconnected by a joint of the type shown in Figs. 2 through 5.

Referring in detail to Figure l, a cylindrical conductor suitable for a core of a concentric transmission line comprises two members I and The member I is 2 having the same diameter. provided with a portion near its end in which two diametrically opposite sectors each spanning preferably degrees of circumference are cut away to form longitudinal channels 3. The member 2 has one end bored hollow for a distance preferably having a length equal to that of the recessed channels 3,-this bore being of the same diameter as the bottom of the channels 3. tubular walls formed in the bored-out portion of themember 2 are then cut away to form two pro ecting fingers 4 which inand engage the walls and nels 3 in the member I. tions I and 2 fingers 4 slide of the channels moved together tance, while still tact between the joint. being the same thereis-no difierence in the diameters of the conductor-om opposite sides of this sliding joint.

Referring in detail to Figs. 2 "and 3,-a tubular bottom of the chan- Thus, when the porin and closely engage the walls or apart for asubstantial dismaintaining good electrical conengaging surfacesof the sliding -'conductor II which may constitute the sheath are brought together so that the" 3, the members I and 2 may be The diameters of the members I and 2' of a concentric transmission line has its wall thickness reduced by one half for a distance back from one end substantially equal to the length of the channels 3 in Fig. 1. In addition the tubular portion of reduced diameter is cut away to form three projecting fingers separated by open spaces, the fingers and spaces each occupying preferably 60 of the circumference of the tube.

Referring to Figs. 4 and 5, a second tube conductor 15 of the same diameter outside and inside as the member H in Fig. 2, and which may constitute a portion of the sheath-conductor of a concentric transmission line, has recesses or channels l6, each occupying preferably 60 of its circumference and having a depth preferably equal to one-half the Wall thickness of the conductor 45 cut in its interior surface. The axial length of the channels I6 is slightly greater than that of the fingers I2 in Fig. 2. The radial and circumferential dimensions of the fingers l2 in Fig. 2 and the channels 16 in Fig. 4 are preferably made such that the fingers l2 can slide with all contiguous surfaces engaging within the channels I6.

It will be evident that the tube II of Fig. 2 and tube l of Fig. 4 are adapted to form the respective halves of a sliding joint in a continuous conductor. Since the inside and outside diameter of the members I l and 15 are the same, it will be evident that there is no variation of such diameter in crossing this sliding joint from one side to the other.

While the exterior and interior diameters of both the cylindrical conductor of Fig. 1 and the tubular conductors of Figs. 2 and 4 suffer no alteration in passing from one side of the sliding joint to the other, there will be a slight variation in impedance in passing from point to point axially along the joint. Nevertheless this variation of impedance will be substantially smaller than was the case where conductors of the prior art employ sliding joints of a type in which one tube or cylinder slides and telescopes within another of somewhat different diameter.

While I have illustrated the principles of my invention in a cylindrical conductor having only two projecting fingers, each one spanning 90 of the circumference of the conductor and have illustrated it by a tubular joint having three fingers spanning 60 circumferentially, it will be evident that the number of fingers and the associated. recesses may be increased above these values and made as large as maybe desired by decreasing the number of degrees of circumference spanned by each finger. When the number of fingers is thus increased, the impedance becomes more and more nearly uniform throughout the axial length of the joint regardless of the degree of axial displacement of two members of the joint.

While I have illustrated the principles of my invention by describing a specific embodiment, it will be evident to those skilled in the art that the principles thereof are of a broader application in phases which will be evident.

I claim as my invention:

1. A concentric transmission line comprising a core conductor provided with a sliding joint comprising a first member having a plurality of arcuate projecting fingers of conducting material separated circumferentially by gaps, and a second member of conducting material having the same outside diameter, and having a plurality of circumferentially displaced channels positioned and dimensioned to engage said fingers in sliding contact,'the two portions of said linear conductor projecting in opposite directions from said joint, and a sheath conductor comprising two tubular portions of the same inside and outside diameters one said portion having projecting fingers circumferentially separated by gaps and the other having channels adapted to engage the surfaces of said fingers in sliding contact.

2. A concentric transmission'line comprising a core conductor provided with a sliding joint comprising a first member having a plurality of arcuate projecting fingers of conducting material separated circumferentially by gaps, and a second member of conducting material having the same outside diameter, and having a plurality of circumferentially displaced channels positioned and dimensioned to engage said fingers in sliding contact, the two portions of said linear conductor projecting in opposite directions from said joint, and a sheath conductor comprising two tubular portions of the same inside and outside diameter, one said portion having projecting fingers circumferentially separated by gaps and the other having channels adapted to engage the surfaces of said fingers in sliding contact, the interior diameter of said fingers being the same as that of said tubular conductors and the exterior diameter of said fingers being less than the exterior diameter of said tubular portion.

3. A concentric transmission line comprising a core conductor provided with a sliding joint comprising a first member having a plurality of arcuate projecting fingers of conducting material separated circumferentiall by gaps, and a second member of conducting material having the same outside diameter, and having a plurality of circumferentially displaced channels positioned and dimensioned to engage on three sides said fingers in sliding contact, the two portions of said linear conductor projecting in opposite directions from said joint, and a sheath conductor comprising two tubular portions of the same inside and outside diameters one said portion having projecting fingers circumferentially separated by gaps and the other havin channels adapted to engage on three sides the surfaces of said fingers in sliding contact.

CYRIL E. MCCLELLAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 589,708 Flint Sept, 7, 1897 889,786 Keiner June 2, 1908 981,500 Torgerson Jan. 10, 1911 1,001,376 Elsas Aug. 22, 1911 1 170,959 Campbell Feb. 8, 1916 1,305,311 Sheldon et al. June 3, 1919 1,552,262 Betz Sept. 1, 1925 2,044,580 Leach June 16,1936

2,125,816 Reynolds Aug. 2, 1938 2,297,390 Burger Sept. 29, 1942 FOREIGN PATENTS Number Country Date 128,226 Austria May 10, 1932 475,757 Germany May 1, 1929 586,049 France Dec. 20, 1924 

